In order to mount a process-monitoring or process-controlling instrument or the like in a box or on a support rail it is standard practice to make up a mounting plate or bracket specifically for the instrument involved. Such a custom-made device is relatively expensive.
It is also frequently necessary to provide such an instrument with some arrangement for controlling its temperature. In particular, when electronic monitoring devices are mounted outside, whether on a support rail or in an instrument box, it is necessary to prevent the temperature of the instrument from exceeding approximately 70.degree. C. to avoid damage to the semiconductors in the circuit thereof. It is also often necessary to heat the instruments in situations where they are likely to reach very low temperatures, as where viscous or crystallizing fluids are being monitored or controlled. Providing a heater in a normally tightly packed instrument box is difficult without considerably increasing the size thereof. Moreover, it is normally necessary to mount the heater at some distance from the instrument to be heated so that more heat than required must be generated in view of the inefficiency of heat transfer.